Measurement of thermal conductivity of (neutrally and nonneutrally buoyant) stationary suspensions by the unsteady−state method

Abstract

The thermal conductivity of neutrally buoyant suspensions containing polystyrene spheres is shown to decrease with increasing particle concentration and to satisfy Maxwell’s formula up to the investigated concentration of 40% (within the limits of experimental error). However, the thermal conductivity of nonneutrally buoyant suspensions (density difference between suspension components about 1.5%) is shown to be higher (at high concentrations) than predicted by Maxwell’s formula. This is attributed a priori to the wake created by gravity settling of aprticle assemblages. By similarity arguments, the augmentation in the thermal conductivity of unbounded suspensions is seen to be a function of particle concentration, Reynolds number, and Peclet number (both the numbers based on the particle size and its settling velocity). The transient technique (adapted for electrically conducting fluids) was employed in a relative method of determining the thermal conductivity of the unknown liquid relative to